Many electronic devices or systems, such as computers, tablets, and cellular phones, have a power management unit to control power supply voltage for some circuits (e.g., digital circuits) in the device or system. Conventional techniques are available to enable such circuits to operate at a minimum energy point (MEP). The MEP is the power supply voltage at which the circuit may consume the lowest energy per operation. However, as described in more detail below, some conventional techniques may have drawbacks that may make them unsuitable for some applications.